Department secretary Dennis Richardson is involved in deciding who will be given a redundancy. Photo: Jim Rice

The executive level workforce will be slashed by 10 per cent as the Defence bureaucracy fixes its span of control by increasing the number of employees under each of its managers.

Defence has also revealed that it will hand redundancies to staff involved in its two biggest spending projects: the joint strike fighter and submarine acquisition programs.

Employees who have said yes to a redundancy still have time to change their minds.

The breakdown of voluntary redundancies from Defence include 214 from the capability acquisition and sustainment group [formerly the Defence Materiel Organisation], 42 from the science and technology group, 29 from the vice-chief of the defence force group, 19 from the air force and five from the navy.

The trimming of 40 staff from the Defence science and technology group comes on top of 574 jobs already left vacant in a group which had a total headcount, including unfilled positions, of 2300.

Department secretary Dennis Richardson and relevant group heads decided who would receive redundancy.

A Defence spokesman said there was no plan to offer further redundancies to any of the 700-plus civilian workers who missed out.

Speaking broadly of the cuts, the spokesman said Defence had focused on ensuring capability was maintained, and offers were only made where it would be "consistent with organisational needs and requirements".

The spokesman said "a small number" of employees working on joint strike fighter and submarine aquisition would be offered redundancy.

Professionals Australia ACT spokesman David Smith said the redundancies, if they went ahead as outlined, would do extraordinary damage to Defence.

"Supposedly the organisation wasn't going to reduce staffing in critical roles, yet we are seeing redundancies being offered to engineers, scientists and technical specialists in long-term acquisition and sustainment projects," Mr Smith said.

"In some cases it's in areas where Defence has no back-up depth in relevant expertise.

"It will be expensive, both in the short and long-term, and risky from both a safety and capability availability perspective."

He said the Commonwealth might hire some of the redundant staff back as contractors at two or three times the cost of their ongoing salary "if they were lucky", but will have lost the "internal expertise forever".

"He needs to back these words up with actions and step in for another invisible Defence Minister [Marise Payne].

"If the offers being made are accepted, submarines, as an example, would have no current depth in a critical discipline – naval architecture."

The redundancies are part of implementation of recommendations from the First Principles review announced in April.

The government and Defence agreed to reduce Defence's numbers through redundancies and natural attrition by 1650 civilian workers, leaving the final workforce at somewhere between 17,000 and 18,000 staff.

The review found that Defence had up to 12 layers of management between Mr Richardson and his front-line staff.